In Genesis, the Flood waters prevailed for 150 days before beginning to recede.
Genesis 7:24 states that the waters prevailed upon the earth for 150 days. Genesis 8:3 then says that the waters receded after those 150 days. This is a distinct time marker from the forty days and forty nights during which rain fell, a distinction that is frequently lost in simplified retellings.
The larger chronology continues with the Ark resting on the mountains of Ararat on the seventeenth day of the seventh month. Later, Noah opened the Ark's window, sent out birds, and eventually left the vessel when the earth was dry. Some chronological details are interpreted differently because the Hebrew text uses dates and months whose ancient calendar conventions require explanation.
The 150-day figure is therefore best understood as the period during which the waters remained dominant or prevailed, not as the complete time Noah and his family spent aboard the Ark. The narrative extends well beyond the initial rainfall.